景泰-天祝断裂单元与多重特征地震的危险性概率评估

PROBABILITY OF LARGE EARTHQUAKE RECURRENCE ALONG THE JINGTAI-TIANZHU ACTIVE FAULT

基于景泰 -天祝断裂的大比例活动构造填图资料 ,建立了合理的破裂分段地质模型。在此基础上 ,采用地震危险性分析的“实时模型”并考虑断层段之间的相互作用 ,对景泰 -天祝断裂的大震危险性概率作了定量评估。所得结果认为 ,景泰 -天祝断裂的下次大震很可能是毛毛山与金强河两个单元破裂段的组合破裂 ,震级约MS7 5。未来 10 ,2 0 ,5 0 ,10 0a内最可能的发震概率分别是 14%、2 7%、5 6 %和 81%。

Based on the results of large scale geological mapping (1/50000), we established a reasonable rupture-segmentation model for the Jingtai-Tianzhu active fault. The model comprises two large pull-apart basins on both ends of the fault and two relatively large discontinuous structures along the fault.The basins are considered as 'stable barriers' constraining the maximum surface rupture of the Jingtai-Tianzhu active fault, while the two large discontinuons structures are considered as 'unstable barriers'. Thus, the Jingtai-Tianzhu active fault can be divided into three rupture units or segments the Jinqianghe segment, Maomaoshan segment and Laohushan segment with lengths of 34 km, 56 km and 62 km, respectively.Existing evidences show that each segment has its own characteristic earthquakes, and all the segments may rupture together because of the interaction between each other. Using the 'real time probabilty model' and considering the interaction between the neighboring rupture segments, we estimated the recurrence probabilities of large earthquakes along the fault. The results suggest that in the next 100 years, the Laohushan segment has little possibility for an earthquake larger than M S7.2 to occar, whereas the other two segments have some potentialities. In the future, although the pessibility of rupture to occur on Maomaoshan and Jinqianghe segments is random it seems that the rupture on one segment will irritate the rupture on the other segment. That is, the next large earthquake on the Jingtai-Tianzhu fault is most proloably the resault of a combined rupture of the Maomaoshan and Jinqianghe segments. The magnitude is estimated at about M S7.5, and the preferred probabilities in the next 10 , 20, 50, 100 years are 14%, 27%, 56% and 81%, respectively.